The present invention relates generally to the conversion of a polycrystalline article into a single crystal, and, more specifically, to the control thereof.
U.S. Pat. No. 5,427,051--Maxwell et al. discloses an apparatus and method for the solid-state conversion of polycrystalline alumina to single crystal sapphire. In that process, a local energy source, such as a carbon dioxide laser, heats one end of an alumina tube to a temperature approaching the melting temperature of alumina to initiate and automatically propagate solid-state single crystal conversion along the length of the tube. To prevent thermal shock, laser heat is applied in a ring around the tube by rotating the tube, and in one trial the tube is slightly translated in addition.
The configuration of an article and the application of the heat thereon affect whether or not single crystal conversion is obtained without undesirable thermal shocking.
Accordingly, there is a need for an improved conversion and control process for conversion of a polycrystalline article into a single crystal.